1. Field of the Invention
Connections to the Internet.
FIG. 1 illustrates a typical Customer Premises Network (CPN) 1-100, communicating with the Internet 1-101. The CPN connects to the Internet in the typical manner, through a set of Internet Service Providers, i.e., the ISP Access Clouds ISP-1, ISP-2, . . . ISP-n. The term Access Cloud (often referred to as an Internet link) is used here to distinguish from other, more general terms that have been used to denote Internet connections, but those more general terms also may introduce different, unwanted connotations.
The elements of the entire Internet-ISP Access Cloud connections-CPN system include: The Internet represented as the upper cloud icon INTERNET, the ISP-1 Access Clouds [ISP-1-2-3-4], and the Customer Premises Network that includes a prior art Multihoming System (MHS) connecting the ISP access clouds to Customer User Equipment (CPE). The CPE usually has a Customer owned Hub, Switch or Router connected to a multiplicity of Customer USER servers, computers, work stations and the like, represented here by USER-1, 2, . . . USER m. The Customer Premises Equipment (CPE) resides in the CPN, as does some ISP-owned equipment, indicated by the overlap between the ISP Access Clouds and the CPN.
Each ISP-n Access Cloud has a communication path or connection for Internet traffic (indicated by double-headed arrow ISP-n) that is identified as such by the MHS. As shown in FIG. 2 below, the ISP-n connection from the MHS to the Access cloud is usually a single router (router-n) owned by the particular ISP but located in the customer-premises, a “last mile” link e.g. T1, DSL connecting router-n to a phone company central office or ISP-n point of presence, an Internet router at the ISP-n point of presence (Aggregation-router-n), and all the neighboring routers belonging to ISP-n up to the point where ISP-n connects to another ISP. Each ISP-n, router-n combination is represented by the ‘ISP Access cloud’ icon named, e.g., ISP-1. As shown in FIG. 1, each ISP Access cloud, ISP-n, forms a uniquely identified communication path between the MHS and the Internet.
The communication path ISP-1 through the first ISP Access Cloud consists of the first link or connection to the MHS (the overlap of the Access Cloud and the Customer Premises) and a second link or connection to the Internet (the overlap of the Access Cloud and the Internet cloud.
On the other side of the MHS there are connections to the CPE in the CPN. In the example shown in FIG. 1, customer premises equipment (USER-1, USER-2, . . . USER-M) accesses Internet traffic (double-headed arrows) by separate connections to the MHS through a router, hub or switch. Each of the connections to the MHS from USER equipment may also include a separate firewall (not shown).
Each of the MHS-access cloud connections may also have Ethernet switches, routers or hubs interposed between.
The Access Clouds are shown partly shared by the Internet and partly shared with the CPN indicating that equipment identifying each ISP is distributed, with some Customer Premises equipment (e.g., usually a router) located in the customer premises 1-104. In the CPN of FIG. 1 Multihoming system (MHS) 1-106 is the entity within the CPN directly communicating with the ISP Access Clouds on the one side and CPN User equipment USER-1, USER-2, . . . USER-M (servers, PCs, workstations, etc.) communicating directly with the MHS.
FIG. 1 represents what is typically found in a CPN ranging from a moderate size to enterprise-wide Customer Premises Network incorporating a Multihoming System (MHS) connected to the Internet through a parallel multiplicity of ISP Access Clouds (links).
Definition of an ISP Access Cloud
Referring to now to FIG. 2, a more detailed diagram of a typical ISP Access Cloud lb-100 is shown. An Access Cloud is that collection of elements, which are jointly responsible for delivering Internet traffic to and from the Customer Premises Network 1-100. The first four elements of that collection are a series or chain including, in this example, Customer Owned Ethernet switch lb-102, ISP-owned customer premises router lb-104, a Telco facility lb-106 providing a wide area line (DSL, T1, T3, Wireless, etc), and an ISP point of presence router lb-108. Note that in most cases, some Customer Premises Equipment (CPE) lb-102, although physically located at a Customer site, will belong to the ISP Access Cloud lb-100. After the router lb-108, communication to the rest of the Internet proceeds by parallel paths, e.g., ISP backbone routers lb-110, 112. If any one element of the series chain in an ISP Access Cloud fails, Internet traffic will not be successfully routed through the ISP Access Cloud to the Customer Premises Network. Hence the entire ISP Access Cloud forms a single reliability chain.
FIG. 2 does not cover all cases exhaustively, as ISP Access Clouds are extremely diverse; however it is typical. What is common in all cases is that many routers lb-108, 110, 112. Ethernet switches lb-102, and sometimes phone company switching equipment lb-106, are involved in the reliability chain, some on customer premises, some on Incumbent Local Exchange Carrier (ILEC) premises, with the majority of routers lb-108, 110, 112 being on ISP premises.
In terms of reliability An ISP Access Cloud can be only in one of two states: UP or DOWN.
In the UP state, when all, the elements in the reliability chain are functioning, Internet traffic is successfully delivered to multiple destinations in each direction.
When at least one element in the reliability chain fails, the ISP Access Cloud will be in the DOWN state.
Note that unlike traditional networks prior to the Internet, the reliability chain spans multiple domains of responsibility. In FIG. 2, there are 3 domains: a) the customer (who owns and controls the CPE router and CPE Ethernet switch), b) the Incumbent Local Exchange Carrier who delivers T1 or DSL lines wholesale to an ISP (Telco facility lb-112, and c) the ISPs themselves (including the ISPs hub, switch or router, e.g., router lb-104).
Typically, the MHS maintains a list of User-IP Address (UIA-1, UIA-2 . . . UIA-m), which is a sub-set of the Internet's Destination IP address list. For the particular CPN 1-100, the Internet ‘cloud’ includes a Designated List of active ISPs (servers) denoted as ISP [N]. The members of that set may be enumerated as ISP-n, for n ranging from 1 to N.
Elements of Typical ISP Access Cloud
FIG. 2 shows elements of a typical ISP Access Cloud, these elements include: more routers to internet; ISP back bone router[s]; ISP Point of Presence router; Telco facility: Wide area line (example DSL, T1, T3, Wireless link. On the Customer Premises, a Router; Ethernet Switch; Customer Premises Network; MHS, router & Users.
Prior Art Internet Connection Reliability Measures
Periodic ICMP Requests to Fixed IP List Configured by User
Some existing prior art in ISP Access Cloud status detection involve includes sending periodic ICMP (Internet Control Message Protocol) Echo requests to the fixed list of IP addresses, which is maintained and stored by the CPN, generally in the MHS unit memory storage system. This is a common process well known in the art.
2. Description of the Related Art
Drawbacks of Prior Art Reliability Measures
When these requests are sent through a specific ISP, and fail to elicit an ICMP Echo response, that ISP is declared down. A major drawback of the ICMP request approach in previous systems is that it is unreliable in common situations.
One common situation arises because of router blocking of ICMP packets. Many ISPs configure their routers to block (i.e. drop) ICMP request packets, especially during times when the Internet as a whole or a single ISP is experiencing problems.
When this happens the ICMP requests will time out and the Users MHS will falsely conclude that the ISP is DOWN, even though it is really UP.
A second drawback of previous systems is that the user has to configure a list of destination ISP addresses that need to be checked. The User usually configures this fixed List as part of their normal setup and/or operation procedures. This is an extra burden on system operations personnel.
A third drawback of such previous systems is that once the list of ISP destination addresses is generated, the list is fixed. Over some sustained time period, some or all of the machines supporting the addresses on the fixed list can be taken out of service and be replaced by a machine with a different address providing the same communication path. In that case a false DOWN indication would be detected by an MHS relying on the ICMP packet.
A fourth drawback in the previous systems is non-randomness of flows with systems relying on cache storage of flows. The ICMP requests involve fixed values in the IP address fields that do not change over time. Because of this the following class of fault conditions will not be detected by such a system. Under hostile conditions on the Internet, sometimes these caches storing flows fill up, and new flows are no longer admitted into the router. Old flows will continue to appear to function though, including the ICMP request and response packets. The multi homing system in this case will report a false UP status, i.e. It will fail to detect a true ISP-Access Cloud DOWN status.
It is highly desirable to have a reliable method of detecting the communication status of a network connection as UP or DOWN in the presence of the conditions described above.
A system of reliably verifying UP/DOWN status of a particular ISP is greatly desired and would provide more robust Internet communications for users and suppliers.